Hydraulic fracturing is a common stimulation technique used to enhance production of fluids from subterranean formations. This technique is commonly used to enhance the production of methane from coal bed wells.
In hydraulic fracturing, a fracturing fluid is pumped at high pressures and at high rates into a wellbore to initiate and propagate a hydraulic fracture. The fracturing fluid used to initiate and propagate the fracture is commonly known as the “pad”. The pad may contain a fine particulate having a high apparent specific gravity, such as fine mesh sand, for fluid loss control, or larger grain sand to abrade perforations or near-wellbore tortuosity. Continued pumping extends the fractures.
Once the fracture is initiated, subsequent stages of viscosified fracturing fluid containing suspended proppant are pumped into the created fracture. The fracture generally continues to grow during pumping and the proppant remains in the fracture in the form of a permeable pack that serves to prop the fracture open. Once the treatment is completed, the fracture closes onto the proppant which maintains the fracture open, providing a highly conductive pathway for hydrocarbons and/or other formation fluids to flow into the wellbore.
Natural fractures in formations often create migratory channels for the fracturing fluid wherein the proppant, suspended in the fracturing fluid, settles out of the fluid. Well productivity is often compromised therefore since the pumpable job size is limited and leak-off to the natural fracture cannot be controlled. Previous attempts of introducing conventional proppant into natural fractures to seal off the fractures have used 40/70 or 100 mesh sands in slickwater-type fluids to control fluid loss. Such materials, however, display an excessive settling rate from the suspension.
Improvements in hydraulic fracturing techniques exhibiting minimal fluid loss to natural fractures are therefore desired. Such improvements, in turn, will render an increased effective propped fracture length in naturally fractured reservoirs, thereby improving stimulation efficiency and well productivity.